1. Field of the Invention
This invention relates to tree harvesters.
2. Description of the Prior Art
My earlier U.S. Pat. No. 4,416,311 discloses a tree harvester which enables two trees to be delimbed simultaneously.
The harvester described in such patent incorporates a main boom on the machine; a secondary boom, supporting the grapple and shear assemblies, telescopically mounted on the main boom; and a delimbing assembly movably mounted on the main boom and operable so that as the secondary boom is extended forwardly, the delimbing head moves rearwardly along the main boom at approximately the same speed.
This harvester has proved to have considerable advantages over previously known machines (examples of which include those described in Canadian Pat. Nos. 1,046,908 and 1,051,756 of Eaton Yale Ltd; U.S. Pat. No. 3,905,407 assigned to Clark Equipment Co.; Australian Pat. No. 496860 of Eaton Yale Ltd.; and Australian Pat. Nos. 474858 and 475520 of R. L. Windsor & Son Pty. Ltd.). However, it is considered that a number of improvements can be made to that harvester.
On that harvester, the secondary boom is extended e.g. 2-4 meters, to enable a length of e.g. 4.8 meters to be delimbed in each delimbing operation. In certain applications it is considered that this forward extension places the weight of the trees too far forward of the centre of gravity of the harvester, unbalancing it.
In another area, it has been found that where the grapples are holding two trees of markedly different diameters, the smaller tree may not be on the bottom knives of the delimbed head, reducing the effectiveness of the latter.
It is also considered that the scissor-type action of the shearing head does not cut the trees as cleanly as possible, especially when docking the trees to length.
In addition, the limited movement of the shear and grapple heads relative to the machine does not enable the harvester to harvest trees which have fallen or are leaning away from the harvester.
Finally, when de-limbing the upper sections of the trees, these sections are often not strong enough to enable the trees to be fed through the shear and grapple heads to enable them to be docked to length and so one length of timber from each tree may be wasted.